Liposomal formulation and antitumor activity of 14-O-palmitoyl-hydroxyrubicin

Enhanced tumor delivery and antitumor activity of palmitoyl rhizoxin using stable lipid emulsions in mice

PURPOSE

A highly lipophilic antitumor agent, 13-O-palmitoyl-rhizoxin (RS-1541), was incorporated into lipid emulsions of various sizes consisting of triglyceride ODO and surfactant HCO-60. Pharmacokinetics, toxicities, and antitumor activities were evaluated after intravenous administration to mice bearing subcutaneously inoculated M5076 sarcoma cells.

METHODS

The levels of RS-1541 in the plasma and tissues including tumor, were determined by HPLC. The maximum tolerated dose (MTD) was estimated by toxic death and change in body weight. The decrease in tumor diameter was measured for antitumor activity.

RESULTS

There existed large variations in pharmacokinetics of RS-1541, depending on the size of emulsion particles. Compared with a colloidal solution (reference solution), the small (110nm) and medium (230nm) size emulsions showed high concentrations of RS-1541 in the tumor, while the large emulsions (350nm-630nm) exhibited low concentrations. The MTD of RS-1541 was reduced, when incorporated in the emulsions larger than 220nm in size. At MTD, each size of emulsions (70nm-380nm) effectively retarded the tumor growth and increased survival time. The maximum effect was achieved for the 220 nm emulsions.

CONCLUSIONS

When particle size is properly selected, these emulsions could be promising and effective as an injectable carrier for lipophilic antitumor agents in order to enhance the tumor delivery and efficacies while reducing toxicities.

Polyethylene glycol modified phospholipids stabilize emulsions prepared from triacylglycerol

A stable lipid-based carrier system containing a triacylglycerol core has been developed. This has been achieved by homogenization of corn oil (primarily triacylglycerol) in the presence of phosphatidylcholine (PC), preformed 100 nm liposomes prepared from PC/cholesterol (55: 45; mol:mol) and polyethylene glycol modified phosphatidylethanolamine (PEG2000-PE). The lipid/liposome mixtures were emulsified using a microfluidizer, and the resulting particles could, depending on the phospholipids used and the addition of cholesterol, be designed to exhibit a uniform mean particle size of less than 100 nm (as measured by quasielastic light scattering). The presence of an oil core within the emulsified lipid preparation was confirmed by freeze-fracture and cryoelectron microscopy. Stability of the resulting PEG2000-PE-coated triacylglycerol emulsion was determined by several techniques including (1) time dependent changes in light scatter determined by measuring changes in absorbance at 600 nm (decreases in absorbance are indicative of unstable oil emulsions), (2) column chromatography procedures evaluating the migration of incorporated lipids, specifically PEG2000-PE and triolein, after emulsions were incubated at 37 degrees C in the presence and absence of serum, and (3) in vivo plasma clearance data demonstrating that the lipid mixtures were maintained at ratios specified prior to i.v. administration. This emulsion technology has been used to prepare formulations of several water insoluble compounds, such as the drugs taxol and dibucaine and the lipophilic dye sudan IV.

Design and tumor targeting of anthracyclines able to overcome multidrug resistance: a double-advantage approach

A novel, 'double-advantage approach' to developing more effective chemotherapies will be reviewed. This approach is based on a presumption that analogs designed on a sound hypothesis, and combined with a rationally selected drug delivery system, will optimize antitumor activity by creating drugs that are more active and that can be more specifically targeted to tumors. In the design of drugs superior to doxorubicin, we have focused on typical multidrug resistance and new anthracycline analogs, whose uptake is not affected by P-glycoprotein. Analysis of structural elements of anthracyclines affecting activity against multidrug resistant tumors and affinity for liposomes will be discussed. Annamycin, a lipophilic anthracycline analog, was selected for further preclinical development as a liposomal formulation and demonstrated, in the initial biological evaluation, high activity against tumors resistant to doxorubicin.